GFCIs detect ground faults, i.e., electric leakage, and automatically trip so that the line contact disconnects from the output contact to avoid an electric shock.
GFCIs may have operational faults caused by various reasons. When the operational faults occur, the electrical and mechanical parts of the device fail to disconnect. The operation faults may be caused by wear and tear of the mechanical parts, erosion, overload caused by improper assembly, mechanical misuse, or electric surge such as a lightning strike. Malfunction of the sensor, detector, switch, trip mechanism, and unstable power supply will all cause operation faults. Short circuit and open circuit resulted from the normal wear and tear or the end of life of the electrical parts cause operation faults as well. When GFCIs have operation faults, they fail to trip and cut off the power. As a result the user may still suffer injury from electric shock.
U.S. Patent Application Publication 2006/0018059 A1 discloses a circuit breaker having a test circuit with one or two indicators, an arc fault signal generator, and first and second test switches.
This type of conventional circuit breaker has disadvantages. First, the interrupter must be triggered manually and periodically, which adds work intensity. Especially when one needs to work with a large number of interrupters, it requires huge work load. Second, if the interrupter fails between the two tests, electric hazard may still occur. Third, if the interrupter fails, it does not provide any alarm signal before the simulated test. Fourth, simulated test requires cutoff of the power supply, which may be inconvenient for the user.
Several U.S. patent application publications disclose circuit protection devices that have self-testing function. However, these devices use high cost parts and have low stability because of the design. Additionally, these devices may not trip and disconnect from the electric power when operation faults occur or the warning signals are given.
U.S. Patent Application Publication 2005/0212522 A1 discloses a circuit protection device which performs self-testing every half-cycle via a test circuit. The circuit protection device does not indicate when the device operates normally.
U.S. Patent Application Publication 2005/0243484 A1 discloses an electric leak breaker having a self-test unit for periodically testing whether the leakage detecting unit or the driving unit is normally operating. The circuit protection device detects malfunction of certain electric units with no indications of the operation status of the other parts or the self-test unit.
U.S. Patent Application Publication 2006/0126522 A1 discloses a self testing fault detector having a controller adapted to perform periodic status tests on a protection circuit without interrupting power to the load. The fault detector performs self test on the fault detection and circuit tripping portions of the device through a two-stage test. The fault detector may fail to signal or trip when the operation fault has occurred.